So-called single-journal compasses are known from DE-C 29 11 015 and GB-C 1,170,243. In these single-journal compasses having a compass top in which the compass legs rotate together about a pivot formed as a screw, the screw causes axial frictional clamping at the apex of the connected compass legs, in that, in interaction with a counter-nut or with a counter-thread, the friction surfaces of the legs are squeezed together.
Both the previously known compasses require the use of relatively expensive metal screws. Additionally, the two previously known compasses do not have straight guiding of the compass top; the compass top thus assumes different angles relative to the drawing plane depending on the angle of opening of the compass legs. This lack of straight guiding makes use of the compass difficult since the compass top constantly has to be positioned during use.
A drawing instrument, in particular a drawing compass or dividers or callipers, is known from DE-C 27 33 978. In this case, an axial frictional clamping is likewise produced by a large-area leg top and by a screw with a counter-nut. Furthermore, an additional punching plate made of steel is provided for the straight guiding of the compass top.
The three parts mentioned, screw, counter-nut and punching plate, make the compass expensive and lead to complicated assembly of the individual parts of the compass. Apart from the three parts mentioned which consist of metal, the compass legs must also be made of metal since the compass legs are of narrow design; the use of plastic material for the compass legs is virtually ruled out since these would bend in a non-permissible manner during use.
A compass is already known from DE-C 25 23 046, in which two tightening screws each form a pivot for each of the two compass arms.
Compasses, whose top and legs are attached using a screw, are known from the following publications: DE-A 1411830, DE-C 243002, DD 280072, DE-A 4201854, DE-U 1863371, U.S. Pat. No. 4,858,32E, DE-A 2922999.
The use of screws for attaching the compass leg and the compass top firstly entails the disadvantage of the relatively high cost of the screws. Moreover, when using screws, the axial frictional clamping they cause can only be adjusted or readjusted with difficulty. Moreover, there is the risk that compasses with self-tapping screws without a counter-nut become overturned, thus losing the requires frictional clamping and becoming unusable.